Dynamically interactive nanoparticles in three-dimensional microbeads for enhanced sensitivity, stability, and filtration in colorimetric sensing

Nanoparticle-based colorimetric detection has emerged as a prominent sensing method owing to its unique optical properties. However, direct exposure of metallic nanoparticles (NPs) to environmental elements compromises their stability, sensitivity, and selectivity, hindering their performances as sensing probes and limiting widespread application due to interaction with unwanted external substances. To address these challenges, we introduce a three-dimensional colorimetric sensor platform using a hydrogel bead-based system (BBS) by encapsulating interactive NPs within size-controllable microbeads. In BBS, NPs move freely within the hydrogel matrix to disperse and aggregate, thus allowing for dynamic interactions with analytes and other NPs. This platform enhances the colorimetric sensing system in three key areas: accelerated sensing response, heightened stability, and efficient filtration, outperforming traditional NP probes in external environments. For example, NPs in a BBS of a selected size, prepared at 3.5 kV, complete their color change induced by analytes in just 134 s. Unlike solution-based systems, which are prone to unwanted NP aggregation within a few minutes due to impurities in real samples, NPs in BBS maintain durability for over 50 days. Furthermore, BBS can filter cationic heavy metals by an average of 26.4% in environmental samples (seawater, rivers, streams, and reservoirs) and biomolecule substances by 2.4 mmol/L in human samples (urine and blood). It maintains stable ion concentrations within microbeads, ensuring prolonged stability and lifespan, thus facilitating analyte detection while concurrently filtering out impurities from various real samples. Empirical evaluations demonstrated BBS’s efficacy in detecting five distinct analytes, substantiating its potential for diverse analytical applications.